TMcL

I have a 5D IV and am writing both RAW + JPG files to both the SD and CF cards. Does the camera take twice as long to write to two cards as it would if I only had one card in the slot? In other words, could I get a longer burst if I used only one card and left the other slot blank? I tried some tests at home, with inconsistent results. Both cards are rates at the same 120 MB/sec. Thanks.

SharpShooter Loc: NorCal

Yes, the camera writes both cards at the same time. You can of course program the camera to write in different combinations.
The more the camera has to write the slower it processes.
One thing that really slows it down is noise reduction, especially at long exposers.
Use the card speeds recommended by the manual. Faster is just a waste of money.
SS

jerryc41 Loc: Catskill Mts of NY

The speeds concerned are higher than you can reliably test at home. Would you be willing to give up duplicate files to save insignificant time?

wdross Loc: Castle Rock, Colorado

I know for my Olympus E-M1 mrII, there are at least 9 combinations of setting up the two slots. I would find it hard to believe that Canon and Nikon and other dual slot cameras would be any different. Best thing to do is check the manual.

TMcL

I guess what I was asking is, if I can get a burst of say 10 shots when writing to 2 cards, would I be able to get 20 shots by writing to only one card...

OddJobber Loc: Portland, OR

No.

mwsilvers Loc: Central New Jersey

Certainly not double, but if your buffer gets filled more quickly saving raw and jpeg on two different cards, the number of images you'll get in a burst will suffer a bit.

via the lens Loc: Northern California, near Yosemite NP

The answer is Yes.

TMcL

I'm afraid I don't understand. The RAW/JPG combinations aren't the point. What I am trying to figure out is, if the camera has to write the data to two cards, does it cut down on the number of shots I can fire off before running out of buffer. Thanks.

Jrhoffman75 Loc: Conway, New Hampshire

If maximum burst speed is your goal turn off all in-camera image processing. If you do some online hunting you will see that the latest Canon cameras really slow down when using the lens correction options in-camera.

here's one thread: https://www.dpreview.com/forums/thread/4067783

TriX Loc: Raleigh, NC

[quote=TMcL]I'm afraid I don't understand. The RAW/JPG combinations aren't the point. What I am trying to figure out is, if the camera has to write the data to two cards, does it cut down on the number of shots I can fire off before running out of buffer. Thanks.[/quote

Yes. You can find the exact number of shots in a burst before the buffer fills in a chart in the manual (pg 171) and there is a substantial difference between writing to one vs two cards. Raw =21 shots with the fastest CF card vs 16 shooting raw + JPEG L.

edit: and shooting dual pixel raw reduces the number to 7. BTW, although not stated in the manual, I have found that using the in-camera lens correction reduces the burst speed on my 5D3, so I keep it disabled and do the correction in post - not sure if the same is true for the 5D4. I didn’t see a spec for degradation in the max burst if you write raw to both cards for redundancy, but my 5D3 manual does have a note that says it reduces the burst, but doesn’t specify how much. There may be a similar notation in the 5D4 manual, but I didn’t immediately find it. Maybe another member may know...

bpulv Loc: Buena Park, CA

I use a Nikon D800, but the setup on the card slots is about the same on a Canon. Go into your menus and you should find where you can select different options for your slots including recording the same or different formats on each card and using one card as overflow for the other so that if card 1 fills up, the camera will continue recording on card 2 so that two 64Gb cards effectively become 128Gb.

brooklyn-camera I Loc: Brooklyn, NY

I shoot with the 7D MKII which has two slots (SD & CF). This camera you can set up how they record on both at the same time or either and type of format. I shoot both cards in case one should fail or I drop it in my coffee or whatever.

TheShoe Loc: Lacey, WA

Does the same apply if your dog eats your card?

gvarner Loc: Central Oregon Coast

Writing to the cards is done simultaneously. There is no time difference with two cars versus one card.